1. Field of the Invention
The present invention relates to a shutter for a camera.
2. Description of the Related Art
Although a shutter for a camera is available in various styles and types, as one type there is a shutter for a camera provided such that an aperture of a lens is closed in a state in which a plurality of sheets of sectors are closed and a hole for exposure is opened at a central portion thereof by pivoting the sectors. According to opening and closing operation of the sectors, a base portion of each of the sectors is pivotably supported, a drive pin of a sector drive lever is engaged with a drive hole portion provided at a position apart from the support point by a predetermined distance and the sector can be opened by pivoting the lever and can return to an original position by spring force.
FIG. 8 shows the principle of a shutter drive apparatus for operating a shutter to open and close two sheets of sectors according to a conventional technology and a description of the shutter drive apparatus is as follows. Two sheets of sectors 83 are attached between a shutter base plate 81 and a rear plate 82 to thereby enable to open and close lens apertures 81a and 82a. The shutter base plate 81 and the rear plate 82 can be fixed to be apart from each other at an interval capable of installing the sectors pivotably by screws 84, Respective elements of the shutter drive apparatus are provided on a front face (upper face of FIG. 8) of the shutter base plate 81.
First, a sector drive lever 85 formed with projected portions on both sides of a plate-like member formed substantially in a heart-like shape, is provided at a vicinity of a central portion of the upper face of the shutter base plate 81. According to the sector drive lever 85, a bearing portion 85a provided to project at a pivotal center portion thereof is fitted to a support shaft portion 81b provided to project from the upper face of the shutter base plate 81. A sector drive pin 85b is provided to hang down from a vicinity of a top portion of a lower face of the sector drive lever 85 and the pin passes through an arc groove portion 81c formed in the shutter base plate and is engaged with an oval groove portion 83a of the sector. Further, respective sectors constituting the sector 83 are pivotably supported by pivotal center holes 83b and support pins 81d provided to project from a rear face of the shutter base plate. The respective support pins 81d stably support respectively the sector 83 by being engaged with through holes 82b provided at the rear plate 82.
The sector drive lever 85 is biased in the counterclockwise direction by a spring 86, thereby, the sector 83 is biased in a direction of closing the shutter 83. A drive coil 87 constituted by winding a coil in a spiral shape and solidifying the coil in a doughnut-like shape, is fixedly attached to a rear face of an ear portion 85c formed on a side of the sector drive lever 85 opposed to a position attached with the spring 86. One lead wire 87a of the coil 87 is connected to an outer peripheral portion of the coil and other lead wire 87b is connected to an inner peripheral portion thereof. When electricity is conducted from a drive circuit 88 to the coil 87, there is produced magnetic flux an upper side of which constitutes an S pole and a lower side of which constitutes an N pole, for example. Conduction of electricity to the coil 87 can be controlled by the drive circuit 88 to thereby enable to arbitrarily open and close the shutter.
The drive coil 87 is also pivoted centering on the support shaft portion 81b by pivoting the sector drive lever 85 and a pair of permanent magnets 89 and 90 in a shape of a thin plate are provided on a pivotal locus of the center of the coil. These permanent magnets are fixedly attached onto the upper face of the shutter base plate 81 and the one magnet 89 is disposed on a forward side of the pivotal locus of the coil 87 in the clockwise direction at an initial position and is pasted such that an upper face thereof constitutes an N pole. In contrast thereto, the other permanent magnet 90 is disposed on a rearward side of the pivotal locus of the coil 87 and is pasted such that an upper face thereof constitutes an S pole.
Since the constitution is constructed in this way, when magnetic force with the S pole on a downward side is produced in the coil by conducting controlled electricity from the drive circuit 88 to the coil 87, by the operation of the magnetic force, a suction force is operated between the drive coil 87 and the magnet 89 on the front side and a repulsion force is operated between the drive coil 87 and the magnet 90 on the rear side to thereby move the drive coil 87 in the clockwise direction and pivot the sector drive lever.85 in the same direction. Thereby, the sector 83 is opened and an exposable state is brought about. Next, when electricity is made to stop conducting to the drive coil 87, the magnetic force is extinguished, the sector drive lever 85 returns to the original position by the spring 86 and the shutter is closed.
According to the shutter drive apparatus of the conventional example, the sector drive lever 85 and the drive coil 87 are disposed on different planes and accordingly, there poses a problem in which areas on the planes become large. Further, in addition thereto, the sector drive lever 85, the drive coil 87 and the permanent magnets 89 and 90 are provided at respectively different heights and accordingly, there poses a problem in which a thickness of the shutter becomes large by that amount. Further, the sector drive lever 85 is pivoted by pivoting the drive coil 87 per se and accordingly, there poses a problem in which large kinetic energy is needed and accordingly, power consumption is increased.
A supporting plate having an opening is integrated with magnetic field generating elements in the form of a fixed printed board having a plurality of coil patterns substantially disposed in a concentric shape relative to a center of an optical axis of the opening and a movable printed board opposed to (confronting) one face of the fixed printed board and having magnetic field generating elements in the form of a plurality of coil patterns in a similar manner, the movable printed board is made pivotable by conducting electricity to the respective coil patterns acting as electromagnets and the movable printed board is constituted to be capable of opening and closing a sector to thereby enable to realize thinned formation and downsized formation of the shutter.
Polarities of the two printed boards are made the same in directions in which the two printed boards are opposed to each other, further, initial positions of the movable coil patterns of the movable printed board are set to positions deviated from positions of the fixed coil patterns of the fixed printed board in an advancing direction by a predetermined angle, electromagnetic forces produced from the two coil patterns and produced by conducting electricity from a drive circuit repulse each other and the movable printed board is made pivotable in a direction of opening the sector.
The movable printed board is easily pivoted in the direction of opening the sector by providing a cam mechanism for making the movable printed board progress and regress in a direction of the optical axis on faces of the movable printed board and a shutter base plate opposed to each other.
When the sector is opened to an aperture having a size determined by a diaphragm value, the sector is set to stop driving, at this occasion, when electricity is made to stop conducting to the coil patterns by the drive circuit, the electromagnetic forces of the two printed boards are extinguished and a sector lever returns to an original position by biasing force of a spring to thereby close the shutter.
As an example of the cam mechanism, there is adopted a cam mechanism in which end face cams disposed substantially in a concentric shape relative to the optical axis center are provided at either one of the shutter base plate and the movable printed board and cam followers provided to project from the opposed face are provided at other thereof. The end face cams are formed at inclined faces lowering in a direction of pivoting the movable printed board in a direction of opening the sector to thereby facilitate pivoting of the movable printed board.
Further, in any of the above-described means, according to the respective coil patterns, the respective coil patterns are arranged at the respective printed boards in a connected state on the faces of the respective printed boards opposed to each other or on two faces of each of the printed boards and electromagnetic forces of a number of the coil patterns are utilized to thereby provide large drive force.
In arranging the coil pattern of the printed boards, the movable coil patterns of the movable printed board are disposed at positions deviated from the fixed coil patterns by a predetermined rotational angle in an advancing direction at initial positions. Further, ways of winding spirals of coils in coil patterns of the two boards are made to direct in directions opposed to each other in view from the same direction, torque is operated to the movable printed board by repulsion force and force in the optical axis direction is effected by pressing the movable printed board to thereby help pivot the movable printed board by the cam mechanism.
According to other means, drive force in closing the sector is controlled by the drive circuit such that electricity is conducted to the coil pattern of either of the printed boards to direct in a reverse direction, in addition to the biasing force of the spring to thereby enable to shorten a time period of closing the sector by utilizing suction force produced by making polarities at the opposed faces different from each other.
Further, according to other means, as the coil patterns of the respective printed boards, by arranging spirals in the same way of winding in view from the same direction on both of the printed boards, there can be produced electromagnetic force having an intensity twice as much as that in the case in which the spirals are arranged only on faces of the respective printed boards on one side.
Further, according to other means, permanent magnets are arranged on a rear face of the supporting plate in place of the coil patterns of the fixed printed board to thereby enable pivoting of the movable printed board by magnetic force of the permanent magnets and the electromagnetic force produced by the coil patterns of the movable printed board. Although a thickness of the shutter is increased by a thickness of the permanent magnets, the sector can be opened by large drive force since strong magnetic force is provided.